1. Field of the Invention
The invention relates generally to packer setting devices. In particular aspects, the invention relates to the design of devices for setting packers using hydrostatic wellbore fluid pressure.
2. Description of the Related Art
Packers are used to create a seal within the annulus of a wellbore between an interior tubular string and the wall of the wellbore. Packers incorporate an elastomeric sealing element that can be radially expanded to set the packer. The packer may also incorporate one or more metallic slip elements that create a mechanical anchorage between the interior tubular string and the wellbore. Commonly, packers are mechanically set by applying an axial force to the sealing element and slip elements to cause them to be expanded radially outwardly and into engagement with the surrounding wellbore wall. A setting tool can be used to do this. Alternatively, fluid can be pumped down the flowbore of the interior tubular string and the fluid pressure used to axially compress the packer element.
Another method of setting the packer device is by use of hydrostatic pressure. U.S. Pat. No. 6,843,315 issued to Coronado et al., for example, describes a hydrostatically-set packer device having a composite sealing element with large radial expansion capabilities for use in through tubing and open hole applications. This patent is owned by the assignee of the present invention and is, therefore, incorporated by reference. The hydrostatic pressure of the column of fluid within the wellbore is used to provide the setting force for compressing the packer element. However, there are difficulties with the design of setting devices that are used in very deep wells due to the presence of high hydrostatic pressures. In particular, hydrostatic pressures of 20,000 psi or greater are problematic. With such ambient pressures, the setting mechanism can be prone to premature actuation and setting of an associated packer. In addition, certain components of setting devices, such as large volume chambers, are prone to crushing damage at great depths.
The present invention addresses the problems of the prior art.